Never fear, this isn't a complex equation at all! (Why, you'd have to have the sqrt of -1 for that to be the case
).
To get the answer, it is a simple trig "trick" -- i.e., once you see it it's not that hard. Think about what the inverse tangent of 12/x represents. It equals some angle from a right triangle whose "opposite" side is 12 and whose "adjacent" side is x (because tan theta is opp/adj). Then you want to find the cos (and sin) of this angle. Well, cos is adj/hyp and sin is opp/hyp -- and from the previous argument, you know both adj and opp, so all that is left is to find the hypotenouse. Just form the triangle ...
Code:
|\
12 | \ hyp
|_(\
x
But from the pythagorean theorum you know that hyp = sqrt(144+x^2). Well, then you can get the system of equations in terms of x without any nasty trig functions, which should make it pretty simple to solve (I'm assuming you can solve systems of equations and the trig was throwing you off ... if not, just ask for an explanation!)
Oh, and an 89 is good for just about anything
Or mathematica, if you have the software (somewhat pricey). But nothing beats pen and paper!